The present disclosure relates generally to aircraft electrical power systems, and more particularly to supplemental electrical power systems and methods for twin engine aircraft.
Modern aircraft include a large number of electrically powered loads. Electrically powered loads include, for example, cabin services, avionics, communications systems, fuel pumps, galley refrigeration, fans, lighting, etc. To provide electrical power for the various loads, an aircraft typically includes at least one generator mechanically coupled to at least one of the aircraft's engine(s). The generator's output electrically powers the aircraft's power distribution system.
In some know twin engine aircraft, each engine has a generator coupled to its gearbox. The main generator may contain a transmission that helps ensure that the generator is driven at a substantially constant speed to produce a substantially constant output. The alternating current (AC) outputs of the two main generators are coupled to the power distribution system to power the aircraft's electrically powered loads. The main generators are sized to be capable of providing enough power for all of the electrically powered loads. A backup generator is also coupled to each of the two engines. The backup generators are used to back up the main generators during abnormal conditions. The backup generators may produce a variable frequency output that may be converted to a fixed frequency. In this case, the variable frequency output power of a backup generator is rectified and supplied to a direct current (DC) bus. The DC bus is connected to an inverter that produces a substantially fixed frequency and magnitude AC output from the DC input. The AC output of the inverter may then be used to power at least some of the electrically powered loads. The backup generators may be required to comply with various regulations, but the backup generators are typically not used under normal operating conditions.